There is a need for the food processing industry to find alternative methods for processing and using eggshells in a way that is beneficial to the environment. In the United States, there are about 190,000 tons of wasted eggshells generated by egg processing and hatchery plants annually. From this amount, about 120,000 tons are generated from egg processing plants and about 70,000 tons are generated from hatcheries. When eggshells are stored at room temperature, they are rapidly degraded causing unpleasant sulphurous odors. Typically, eggshells are disposed in a landfill, currently the most common and economical disposal method. Landfill deposition costs range about $20-40 per ton, where it is permitted. In many states, landfill disposal of eggshells is not permitted. The landfill disposal produces methane, carbon dioxide and other volatile organic chemicals.
Eggshell contains about 4% organic matter and a substantial amount of calcium and other minerals, including magnesium and zinc. Dried eggshell particles contain approximately 94% calcium carbonate, with 39% of the compound being absorbable calcium. Natural calcium sources not only contain calcium but also magnesium, phosphorous and zinc.
U.S. Pat. No. 5,045,323 describes a method for preparing compounds from eggshells, particularly from the chicken eggshell, which could be utilized for medical purposes for treating certain diseases and for replacement of deficient materials in living tissues. The method includes drying eggshells using hot air at a temperature of up to 150° C. The dried eggshells are then ground to a particle size of 10-80 microns. After drying, the temperature is lowered to 50° C. The dried eggshell powder only contains carbonate compounds and does not possess anti-microbial properties.
U.S. Pat. No. 6,176,376 describes a method and apparatus for separating the membrane layers from the inside of eggshells by mixing with water. The eggshell particles and membrane particles are separated for further processing. The eggshell membrane contains about 10% collagen that is used for skin grafts, dental implants, cornea repair and other medical uses. The purified eggshells are also used in paper or agriculture industries as lime substitutes or calcium supplements.
U.S. Pat. No. 5,409,714 describes an anti-microbial agent containing a calcined calcium oxide prepared by calcining oyster shells and/or a calcined product of a calcium hydroxide or hydrated product of calcium hydroxide. The particle size of the product is less than or equal to 74 microns. It can be applied to processed food in a liquid state ranging in amounts from 0.05% to 10% by weight. The product comprises a combination of a calcined calcium oxide type and the calcined product of calcium hydroxide. The ratio of the types of calcium oxide ranges from 3 to 7 parts to approximately 7 to 3 parts. The examples in the disclosure show uses of the product as a preservative of various food articles, namely rice, ice cream, cucumbers, eggs, cuttlefish and edible jellyfish. Since the oyster shells come from the ocean, the mineral content of the shells is not precisely controlled as it is in eggshells because of the specialized formulation of poultry feed. The oyster shell may have a less consistent chemical composition than eggshells and have more heavy metal contamination.
U.S. Pat. No. 2,419,822 describes a process for production of calcium carbonate from eggshells. Eggshells are placed in a drum having rotating internal blades which crush the shells in the presence of hot water. Rotation of the blades is stopped and the drum is drained of water and impurities, and subsequently the drum is closed and the blades are rotated again with the emission of hot air to dry the eggshells. The crushed shells are then removed and ground under oxygen to produce a dry bacteria-free product.
While the foregoing methods of utilizing eggshells and hatchery waste, none can remedy the problem of large-scale disposal of eggshells. The present invention provides an improvement in the art by treating eggshell to provide a dry pathogen-free eggshell powder that has many applications.